Data transmission of radio-frequency signals on mains cables is known. This allows information to be transmitted in addition to or as an alternative to conventional telephony, which is particularly advantageous since electrical networks with mains connections exist virtually everywhere. Particularly for industrial low-voltage networks with busbar systems and distribution busbars, this results in the capability to set up a dedicated data transmission system.
Typically, power is transmitted in industrial systems via busbar systems, which are in turn fed from a transformer that is located in the immediate vicinity. Loads are connected to the busbar system via outgoer cables in the form of individual cables or distribution busbars. Distribution busbars are in turn longitudinally extended and encapsulated solid conductors with a relatively small cross section, which in manufacturing systems are generally fitted horizontally underneath or above the loads that are to be supplied. Furthermore, distribution busbars have outgoers that are arranged in a specific pattern, and to which the loads can be connected by means of so-called tap-off boxes.
Busbar systems and distribution busbars in low-voltage networks are, for telecommunications purposes, conductors with a very high characteristic impedance in the range of several hundred ohms. In addition, power-feeding busbar systems with their high prospective short-circuit currents and very low impedances represent, in particular, low-impedance shorts for signals in the frequency band from 100 kHz to several MHz, in which, for example, modern powerline communication (PLC) systems operate. Consequently, the levels of signals which are fed into the busbar system directly are highly attenuated. In conjunction with the high interference levels which occur in industrial low-voltage networks, protected data traffic is no longer possible with this type of feed even after comparatively short distances of a few tens of meters.
EP 0 889 602 A2 discloses a data transmission system for transmitting data via at least one electrical power cable, with the data being input and output at the end areas of a power transmission cable. Furthermore, DE 44 18 296 A1 discloses network coupling being provided for data transmission via an electrical distribution network with associated filters to the coupling points. Finally, DE 9 504 587 A1 discloses a two-way communication system for power supply networks in a low-voltage network, in which data is transmitted.
Furthermore, JP 01-221028 A discloses a power cable transmission system (PLC) which has load lines with blocking filters which allow current to pass at the mains frequency (50 or 60 Hz) in order to supply power, but which block radio-frequency signals. Furthermore, a logic circuit which carries out a digital data interchange via so-called special lines is arranged between the PLC units which supply the individual load lines.